1. Field Of The Invention
The present invention relates to a group control method for controlling as a group a plurality of motor-driven screens equipped with respective bottom weighting bars or “load bars”. Such screens may be venetian blinds or shades or other analogous blinds or shades. This type of screen is provided with a least one raising cord, connected to the load bar, and winding around a shaft driven in rotation by an actuator. The screens may also be roll-up fabric blinds or shades, or indeed roller blinds or roller shutters. In any event it is necessary for the position of the load bar of a screen to be measured as independently as possible from the position of the screen.
2. Brief Description Of The Related Art
In order to drive a plurality of motor-driven screens, it is known that automatic motor control can be used that makes it possible to manage the screen positions and/or the slat angular positions of the screens of the group in such a manner that each screen has the same screen position and/or the same slat angular position after a group command. The driving is generally achieved by operation of the “master-and-slave” type in which a “master” screen drives the “slaves”, i.e. the other screens of the group. The slave screens reproduce the configuration, i.e. the screen position and/or the slat angular position of the master screen, as described in Application JP-A-08210054. As specified in EP-A-0 913 748, the screen position and/or the slat angular position of a screen can be adjusted by calculating motor or time pulses by means of a microprocessor. Correspondence between those pulses and screen position or slat angular position may be defined directly.
The stroke of a screen is determined by the distance travelled by the load bar between first and second predetermined positions. The first position or “upper limit” generally corresponds to a load bar position in which the screen is fully open. The load bar then reaches a top abutment. The top abutment is a stop position desired by the user. The second position or “down limit” corresponds to a load bar position such that the screen is fully closed. The load bar then reaches a bottom abutment. In the preceding patent applications, all of the screens have substantially the same stroke and the same upper limit positions.
The position of the load bar of a screen is measured relative to a predetermined reference position. In addition, a calibration operation may be provided that makes it possible to define the same reference position for all of the screens of the group after installation. Such a reference position is described as a common specific position corresponding to all of the tops-of-stroke of the screens in the group.
Thus, when a load bar movement instruction is executed for moving the load bars to a precise desired position of the screen stroke, each load bar of the screens of the group moves towards that position defined relative to the common reference position. At the end of the operation, all of the load bars lie at the same position and are aligned. However, if the load bars of the screens of the group are not aligned at the time the instruction is issued, then each load bar moves independently from the other load bars. That results in the movements of the screens of the group not being harmonious due to the variations in amplitudes of movement of the load bars. In addition to the unpleasing appearance, such unevenness does not make it possible to have rapidly information about the synchronization of the screens, and in particular of their counter means, or about the screening states of the other screens in the group.
The same applies when a group command for opening or for closure is executed for a group of screens in which the load bars are not aligned. Alignment of the load bars can be obtained in the end limit position, after movements of various amplitudes.
Alignment of the load bars of roller blinds during an operation is known from US-A-2005/0173080 that describes speed compensator means for two screens of different configurations, which means act so that the load bars of both screens move level with each other when they are caused to move simultaneously. However, when those load bars are not initially level with each other, that system does not make it possible to align the load bars while they are moving.